Wellbore clean up has become an integral part of well completion operation aiming to maximize well productivity from a near skinless wellbore. The awareness has become more widespread with more and more horizontal and sand packed openhole wells being completed with so-called non damaging Drill-In-Fluids (DIF). Although drill-in-fluids control fluid loss and saturation related damage to a great extent, they tend to leave a sticky filter cake containing polymers and Calcium Carbonate particulates which can severely restrict well flow. Acids, oxidizers, chelating agents and enzymes have been often used as wellbore clean up fluids with mixed success. This article demonstrates laboratory and field evidences on superior efficiency of some recently developed bio-enzymes and explains the reason of their not so satisfactory treatment result in some wells. Simulated Reservoir Condition Core Flow (RCCF) and return permeability measurement was the basis of laboratory evaluation and comparison of various clean up formulations, including inorganic/organic acids, oxidizing agents, various enzymes and combination treatments. Mud filter cake was developed by simulating drilling and reservoir parameters. Cleaning treatments were mimicked as per realistic field operation. Photographic evidences were produced on clean up efficiency and final conclusion was drawn based on return permeability. Well treatment methodologies are discussed and production data from over twenty wells/legs were produced, analyzed and compared. An effort is made to analyze unsatisfactory treatment outcome in some of the enzyme treated wells and to establish the best practice approach for wellbore clean up operations.